This invention relates to a telescopic beam, and in particular to a telescopic beam along which a load-carrying tub is movable.
It is known to provide such a telescopic beam with locking means for preventing retraction of the telescopic members comprising the beam. For example, it has been proposed (see DE-OS No. 3 001 420.9) to provide locking elements between each pair of adjacent telescopic members of such a telescopic beam. These locking elements are so designed that the beam can have any desired extended length.
Telescopic beams are often used as inclined hoists and are employed by, for example, roofing contractors and building firms. These beams are intended to enable loads, such as tiles or cement, to be raised. In use, the lower end of a telescopic beam of this type is supported on a fixed point, and the beam is then extended to such an extent that its upper end can be supported on another fixed point. Until it is supported at its upper end, the telescopic beam is, for practical purposes, a girder which is supported at one end only, and which deflects accordingly. The concave side of the beam, therefore, faces the ground. However, as soon as the upper end is supported, the beam becomes a girder which is supported at both ends, so that the convex side of the beam then faces the ground. This is the situation in which a tub (which may be carrying a heavy load) is to ascend on the rails formed by the telescopic beam. The smaller the angle between the ground and the telescopic beam, the greater is the bending load applied to the beam. However, since the telescopic beam has to be designed to cater for the maximum load, it has hitherto been necessary, particularly in the case of inclined hoists, to make use of unusually robust (and therefore expensive) constructions. With such a hoist, the maximum extended length of the beam may be as much as 40 meters. The deflection of the beam is, therefore, considerable; and this increases further under an applied load, particularly when this is located approximately at the mid-point between the two support points. If the length of the beam is then required to be adjusted, the loading applied to the beam can result in jamming between the telescopic members so that relative movement is no longer possible.
The aim of the invention is to provide a telescopic beam which does not suffer from the above-mentioned disadvantages.